CN113031365B - AlGaAs waveguide structure and method for generating super-continuum spectrum by using same - Google Patents

AlGaAs waveguide structure and method for generating super-continuum spectrum by using same Download PDF

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CN113031365B
CN113031365B CN202110389781.8A CN202110389781A CN113031365B CN 113031365 B CN113031365 B CN 113031365B CN 202110389781 A CN202110389781 A CN 202110389781A CN 113031365 B CN113031365 B CN 113031365B
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algaas
height
waveguide structure
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light guide
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CN113031365A (en
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苑金辉
张璐琦
邱石
赖锦涛
颜玢玢
王葵如
周娴
霍佳皓
桑新柱
余重秀
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University of Science and Technology Beijing USTB
Beijing University of Posts and Telecommunications
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University of Science and Technology Beijing USTB
Beijing University of Posts and Telecommunications
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/365—Non-linear optics in an optical waveguide structure
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12035—Materials
    • G02B2006/12078—Gallium arsenide or alloys (GaAs, GaAlAs, GaAsP, GaInAs)

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  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
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Abstract

The invention provides an AlGaAs waveguide structure and a method for generating a supercontinuum by utilizing the AlGaAs waveguide. The AlGaAs waveguide structure comprises: the surface of the AlGaAs substrate is provided with a groove; the AlGaAs light guide layer is arranged in the groove and partially protrudes outwards, the upper surface of the AlGaAs light guide layer is at a first height from the upper surface of the groove, and the lower surface of the AlGaAs light guide layer is at a second height from the upper surface of the groove; by adjusting the width, the first height and the second height of the AlGaAs light guide layer, the curve coincidence degree of the first dispersion curve corresponding to the TE wave and the second dispersion curve corresponding to the TM wave is controlled to reach a first preset curve coincidence degree. The invention solves the problem of polarization dependence of pump light in the prior art.

Description

AlGaAs waveguide structure and method for generating super-continuum spectrum by using same
Technical Field
The invention relates to the field of nonlinear waveguides, in particular to an AlGaAs waveguide structure and a method for generating a supercontinuum by utilizing the AlGaAs waveguide.
Background
The generation of mid-infrared supercontinuum has recently become a research focus and can be applied to the fields of spectroscopy, imaging, biomedicine, molecular detection, radar and the like. The generation of the supercontinuum is a result of a beam of pump light being subjected to a combination of nonlinear and dispersive effects in a nonlinear medium, resulting in a greatly broadened spectrum.
Supercontinuum can be generated in bulk crystals, photonic crystal fibers, waveguides and other nonlinear media. Wherein, the aluminum gallium arsenic (AlGaAs) waveguide is an alloy of aluminum arsenide (AlAs) and gallium arsenide (GaAs), the refractive index of the AlGaAs can be adjusted by changing the component proportion in the alloy, thereby the refractive index difference between the waveguide core and the substrate can be adjusted, and the dispersion characteristic of the waveguide can be optimized. In addition, the bandgap of AlGaAs materials can be tailored to reduce the nonlinear loss caused by the two-photon absorption effect in the communication band. And because AlGaAs exceeds 15 μm wide transparent window and 10 ～17 m 2 The Kerr nonlinear coefficient of the order of/W is considered to be suitable for researching nonlinear materials generated by intermediate infrared supercontinuum (B.Kuyken, M.Billet, F.Leo, K.Yvind, M.Pu.Octave-spectral coherent generation in AlGaAs-on-insulator waveguide [ J.].Optics Letters,2020,45(3):603～606.)。
In the prior art, a waveguide structure is sensitive to polarization of an input pulse signal, so that characteristics such as chromatic dispersion and nonlinear coefficients corresponding to TE waves and TM waves are different. To solve this problem, the polarization mode of the input pulse is generally adjusted by a light polarization controller such as a fiber ring polarizer, a wave plate polarization controller, an electro-optic polarization controller, and a calender polarization controller. However, such a solution to the problem of polarization dependence of the pump light by the optical polarization controller increases the complexity of the experimental system and reduces the experimental efficiency.
Disclosure of Invention
The present invention is directed to an algan waveguide structure and a method for generating a supercontinuum using the same, which can solve at least one of the above-mentioned problems. The specific scheme is as follows:
some embodiments of the present invention provide an algan waveguide structure, where the algan waveguide structure is configured to receive a pulse signal and output a TE wave and a TM wave, and the algan waveguide structure includes:
the surface of the AlGaAs substrate is provided with a groove along the light transmission direction;
the AlGaAs light guide layer is arranged in the groove and partially protrudes outwards, the upper surface of the AlGaAs light guide layer is at a first height from the upper surface of the groove, and the lower surface of the AlGaAs light guide layer is at a second height from the upper surface of the groove;
controlling the curve coincidence degree of a first dispersion curve corresponding to the TE wave and a second dispersion curve corresponding to the TM wave to reach a first preset curve coincidence degree by adjusting the width, the first height and the second height of the AlGaAs light guide layer; the refractive index of the AlGaAs light guide layer is larger than that of the AlGaAs substrate.
Optionally, the cross section of the aluminum gallium arsenic light guide layer is rectangular.
Optionally, the aluminum arsenide in the aluminum gallium arsenic light guide layer is 18% by mass, and the gallium arsenide in the light guide layer is 82% by mass.
Optionally, the width range of the AlGaAs light guide layer is 6.95 to 7.15 μm, the first height range is 3.45 to 3.6 μm, and the second height range is 2.95 to 3.4 μm.
Optionally, the width of the aluminum gallium arsenide light guide layer is 7 μm, the first height is 3.52 μm, and the second height is 3.26 μm.
Optionally, when the wavelength of the pulse signal is 4.07 μm, the first dispersion curve corresponding to the TE wave and the second dispersion curve corresponding to the TM wave each have a zero dispersion point.
Optionally, when the wavelength of the pulse signal is 4.2 μm, the dispersion coefficients of the first dispersion curve corresponding to the TE wave and the second dispersion curve corresponding to the TM wave are 4.857ps/nm/km and 4.859ps/nm/km, respectively.
Optionally, the aluminum arsenide in the aluminum gallium arsenic substrate is 80% by mass, and the gallium arsenide in the aluminum gallium arsenic substrate is 20% by mass.
Optionally, the algan waveguide structure further includes:
controlling the curve coincidence degree of a first nonlinear coefficient curve corresponding to the TE mode pulse wave and a second nonlinear coefficient curve corresponding to the TM mode pulse wave to reach a second preset curve coincidence degree by adjusting the width, the first height and the second height of the AlGaAs light guide layer; and/or the presence of a gas in the gas,
and controlling the curve coincidence degree of a first effective mode area curve corresponding to the TE mode pulse wave and a second effective mode area curve corresponding to the TM mode pulse wave to reach a third preset curve coincidence degree.
Optionally, when the wavelength of the pulse signal is 4.2 μm, the nonlinear coefficients of the first nonlinear coefficient curve corresponding to the TE wave and the second nonlinear coefficient curve corresponding to the TM wave are 0.6067/m/W and 0.6057/m/W, respectively.
Some embodiments of the present invention provide a method for generating a supercontinuum using the algan waveguide structure, including:
designing the width, the first height, the second height and the length along the light transmission direction of the AlGaAs waveguide;
inputting a chirp-free hyperbolic secant pulse with the wavelength of 4.2 mu m, the peak power of 4.8kW and the pulse width of 90fs into the AlGaAs waveguide structure to generate a first supercontinuum corresponding to the TE wave and a second supercontinuum corresponding to the TM wave, wherein the frequency spectrum coincidence ratio of the first supercontinuum and the second supercontinuum reaches a preset frequency spectrum coincidence ratio.
Optionally, the width range of the aluminum gallium arsenic waveguide structure is 6.95 μm to 7.15 μm, the first height range is 3.45 μm to 3.6 μm, the second height range is 2.95 μm to 3.4 μm, and the length range along the light transmission direction is 3.2mm to 3.5mm.
Optionally, the broadband wavelengths of the first supercontinuum and the second supercontinuum respectively exceed 1.95 octaves.
Optionally, when the frequency spectrum is-40 dB, the first-order coherence range of the first supercontinuum and the second supercontinuum is 0.9-1.
Compared with the prior art, the scheme of the embodiment of the invention at least has the following beneficial effects:
according to the AlGaAs waveguide structure, the width, the first height and the second height of the light guide layer are reasonably designed, so that the first dispersion curve corresponding to the TE wave and the second dispersion curve corresponding to the TM wave can be controlled to be highly superposed, and the AlGaAs waveguide structure is insensitive to the polarization of an input pulse signal; the polarization mode of the input pulse does not need to be adjusted, the complexity of an experiment system can be reduced, and the experiment efficiency is improved.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention. It is obvious that the drawings in the following description are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort. In the drawings:
FIG. 1 shows an overall schematic diagram of an AlGaAs waveguide structure according to an embodiment of the present invention;
FIG. 2 shows a schematic cross-sectional view of the AlGaAs waveguide structure of FIG. 1;
FIG. 3 is a graph showing the dispersion coefficients of TE and TM waves output by the AlGaAs waveguide in FIG. 1 as a function of the width of the AlGaAs light guide layer;
FIG. 4 is a graph showing the dispersion coefficients of TE and TM waves output by the AlGaAs waveguide in FIG. 1 as a function of the second height of the AlGaAs light guiding layer;
FIG. 5 is a graph showing the dispersion coefficients of TE and TM waves output by the AlGaAs waveguide in FIG. 1 as a function of the first height of the AlGaAs light guiding layer;
FIG. 6 is a graph showing the dispersion coefficients of TE and TM waves output by the AlGaAs waveguide in FIG. 1 as a function of the wavelength of an input pulse signal;
FIG. 7 shows a graph of the nonlinear coefficients of TE and TM waves output by the AlGaAs waveguide in FIG. 1 as a function of the wavelength of an input pulse signal and a graph of the effective mode areas of the TE and TM waves as a function of the wavelength of the input pulse signal;
FIG. 8 is a schematic flow diagram illustrating a method for generating a supercontinuum according to the AlGaAs waveguide structure shown in FIG. 1;
FIG. 9 shows a supercontinuum graph of TE and TM waves output by the AlGaAs waveguide of FIG. 1;
FIG. 10 shows a first order coherence plot of the supercontinuum of the TE and TM waves output by the AlGaAs waveguide of FIG. 1.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the present invention will be described in further detail with reference to the accompanying drawings, and it is apparent that the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The terminology used in the embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise, and "the plural" typically includes at least two.
It should be understood that the term "and/or" as used herein is merely one type of association that describes an associated object, meaning that three relationships may exist, e.g., a and/or B may mean: a exists alone, A and B exist simultaneously, and B exists alone. In addition, the character "/" herein generally indicates that the former and latter related objects are in an "or" relationship.
It should be understood that although the terms first, second, third, etc. may be used to describe embodiments of the present invention, they should not be limited to these terms.
It is also noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that an article or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such article or apparatus. Without further limitation, an element defined by the phrase "comprising a … …" does not exclude the presence of another like element in a commodity or device comprising the element.
Fig. 1 is a schematic overall view of an algan waveguide structure according to an embodiment of the present invention, and fig. 2 is a schematic cross-sectional view of the algan waveguide structure shown in fig. 1, which is taken along a direction perpendicular to a light transmission direction. As shown in fig. 1 and 2, the algan waveguide structure includes:
an AlGaAs substrate 1, the surface of the AlGaAs substrate 1 is provided with a groove along the light transmission direction;
the AlGaAs light guide layer 2 is arranged in the groove and partially protrudes outwards, the upper surface of the AlGaAs light guide layer 2 is at a first height from the upper surface of the groove, and the lower surface of the AlGaAs light guide layer is at a second height from the upper surface of the groove; controlling the curve coincidence degree of a first dispersion curve corresponding to the TE wave and a second dispersion curve corresponding to the TM wave to reach a first preset curve coincidence degree by adjusting the width, the first height and the second height of the AlGaAs light guide layer; the refractive index of the AlGaAs light guide layer 2 is greater than that of the AlGaAs substrate 1.
According to the AlGaAs waveguide structure, the structural parameters of the AlGaAs light guide layer 2 are controlled, so that the problem of polarization dependence of pump light when the waveguide structure is used for generating a super-continuum spectrum in the prior art can be avoided, a novel AlGaAs waveguide structure is provided, the experimental steps for generating the super-continuum spectrum can be simplified, and the experimental efficiency is improved.
Whether the polarization insensitivity of the AlGaAs waveguide structure can be realized by adjusting the structural parameters of the AlGaAs light guide layer 2 or not can be determined according to actual needs. That is to say, no matter what the specific value of the structural parameter is, as long as the dispersion curve, and/or nonlinear curve, and/or mode area curve of the output TE wave and TM wave are highly coincident when the pulse wave signal is coupled into the algan waveguide structure, the pre-polarization step is not required when the algan waveguide is used to generate the supercontinuum, and the problems in the prior art can be solved, and the corresponding effects can be obtained.
The contents of the above embodiments will be described with reference to an alternative embodiment.
The grooves in the AlGaAs substrate 1 can be obtained by etching and other processes, and the specific structural parameters are matched with the structural parameters of the AlGaAs light guide layer 2. Optionally, the groove is strip-shaped or wave-shaped. The aluminum gallium arsenic substrate 1 is an alloy material of aluminum arsenide and gallium arsenide, wherein the mass percent of the aluminum arsenide is 80%, and the mass percent of the gallium arsenide is 20%. Optionally, the refractive index of the aluminum gallium arsenic substrate 1 is 2.92.
The AlGaAs light guide layer 2 is manufactured in the groove, and in the embodiment, the lower surface of the AlGaAs light guide layer 2 is in contact with the lower surface of the groove. In some optional embodiments, the algan light guide layer 2 may be formed in the groove in a suspended manner. The cross section of the AlGaAs light guide layer 2 is rectangular. Optionally, the overall structure of the aluminum gallium arsenic light guide layer 2 may be strip-shaped or wavy. The AlGaAs light guide layer 2 is made of an alloy material of aluminum arsenide and gallium arsenide, wherein the mass percent of the aluminum arsenide is 18%, and the mass percent of the gallium arsenide is 82%. Optionally, the refractive index of the aluminum gallium arsenic light guide layer 2 is 3.22.
Specifically, the height of the AlGaAs light guide layer 2 is greater than that of the groove, and the height of the light guide layer protruding outwards is a first height H 1 The height of the light guide layer embedded in the groove is a second height H 2 . Optionally, the width W of the algan light guide layer 2 is equal to the width of the groove, and the width direction is perpendicular to the light transmission direction. In this embodiment, the algan waveguide structure is an inverse ridge structure.
Based on the AlGaAs waveguide structure, the structural parameters of the AlGaAs light guide layer 2 are designed through experiments, so that the AlGaAs light guide layer is insensitive to the polarization of input pulses. Specifically, the effective refractive index and the mode area of the aluminum-gallium-arsenic waveguide structure are calculated by utilizing COMSOL simulation software, a first dispersion curve corresponding to a TE wave and a second dispersion curve corresponding to a TM wave are calculated and respectively obtained by a software program MATLAB, and the polarization insensitivity of the aluminum-gallium-arsenic waveguide is judged by judging whether the first dispersion curve and the second dispersion curve reach a first preset curve coincidence degree, namely according to whether the two curves are highly coincided. Fig. 3 to 5 show the influence of three parameter changes of the algaas light guide layer on the dispersion characteristics of TE waves and TM waves, respectively, including:
as shown in FIG. 3, when the width W of the AlGaAs light guide layer 2 is 5 μm, the first dispersion curve of the TE wave is A 1 The second dispersion curve of the TM wave is A 2 (ii) a When the width W of the AlGaAs light guide layer 2 is 6 μm, the first dispersion curve of the TE wave is B 1 The second dispersion curve of the TM wave is B 2 (ii) a When the width W of the AlGaAs light guide layer 2 is 7 mu m, the first dispersion curve of the TE wave is C 1 The second dispersion curve of the TM wave is C 2 (ii) a When the width W of the AlGaAs light guide layer 2 is 8 μm, the first dispersion curve of the TE wave is D 1 The second dispersion curve of the TM wave is D 2 。
It can be seen that when W is less than 6.95 μm, the first dispersion curve of the TE wave is located above the second dispersion curve of the TM wave, and as W increases, the dispersion curves of the two modes gradually approach and the zero dispersion point red-shifts; when W is larger than 7.15 μm, the first dispersion curve of the TE wave starts to be located below the second dispersion curve of the TM wave. When W is 7 μm, the two dispersion curves almost overlap.
As shown in FIG. 4, when the second height H of the AlGaAs light guiding layer 2 is larger than the first height H 2 At 2.26 μm, the first dispersion curve of the TE wave is A 1 The second dispersion curve of the TM wave is A 2 (ii) a When the second height H of the AlGaAs light guide layer 2 2 At 2.76 μm, the first dispersion curve of the TE wave is B 1 Second dispersion curve of TM waveIs B 2 (ii) a When the second height H of the AlGaAs light guide layer 2 2 At 3.26 μm, the first dispersion curve of the TE wave is C 1 The second dispersion curve of the TM mode is C 2 (ii) a When the second height H of the AlGaAs light guide layer 2 2 At 3.76 μm, the first dispersion curve of the TE wave is D 1 The second dispersion curve of the TM wave is D 2 . It can be seen that with H 2 In both modes, the dispersion curve is shifted overall towards the normal dispersion region and the zero dispersion point is red-shifted. Dispersion curve for H due to TM wave 2 Is more sensitive, and therefore the dispersion curves of the two modes are progressively closer and further away from each other. When H is present 2 At 3.26 μm, the two dispersion curves almost overlap.
As shown in FIG. 5, when the first height H of the AlGaAs light guiding layer 2 is larger than the first height H 1 At 2.52 μm, the first dispersion curve of the TE wave is A 1 The second dispersion curve of the TM wave is A 2 (ii) a When the first height H of the AlGaAs light guide layer 2 1 At 3.02 μm, the first dispersion curve of the TE wave is B 1 The second dispersion curve of the TM wave is B 2 (ii) a When the first height H of the AlGaAs light guide layer 2 1 At 3.52 μm, the first dispersion curve of the TE wave is C 1 The second dispersion curve of the TM mode is C 2 (ii) a When the first height H of the AlGaAs light guide layer 2 1 At 4.02 μm, the first dispersion curve of the TE wave is D 1 The second dispersion curve of the TM wave is D 2 . It can be seen that H 1 Influence on the Dispersion Curve and H 2 Similarly, except that the dispersion curve of the TE wave is less affected.
Among the three structural parameters, the dispersion is most sensitive to the width W of the AlGaAs light guide layer. In this embodiment, in order to obtain the polarization-insensitive ridge-type algan waveguide, optionally, the structural parameters of the algan light guide layer 2 in the algan waveguide structure are as follows: w =7 μm, H 1 ＝3.52μm，H 2 ＝3.26μm。
According to the structural parameters in the designed AlGaAs waveguide structure, the polarization insensitivity of the AlGaAs waveguide is further verified through experiments. The verification method is various, for example, by comparing the curve coincidence degrees of the dispersion curves of the TE wave and the TM wave, when the two curves are highly coincident, the polarization insensitivity is represented; and may be further verified in conjunction with a non-linear coefficient curve and/or an effective mode area curve.
As shown in fig. 6, COMSOL simulation software is used to calculate the effective refractive index and the mode field area of the designed waveguide, and then software program MATLAB is used to calculate and obtain the dispersion coefficients of TE wave and TM wave, so as to further obtain a first dispersion curve (i.e. the solid line shown in fig. 6) and a second dispersion curve (i.e. the dashed line shown in fig. 6) of which dispersion coefficients vary with wavelength. It can be seen that the first dispersion curve and the second dispersion curve have relatively flat anomalous dispersion regions, and the dispersion curves of the waves of both modes have a zero dispersion point at 4.07 μm, and the pumping near the zero dispersion point is favorable for generating a broadband supercontinuum.
And comparing the first dispersion curve with the second dispersion curve to obtain the curve coincidence degree of the first dispersion curve and the second dispersion curve, and judging whether the curve coincidence degree reaches the first preset curve coincidence degree. The coincidence degree of the first preset curve is the lowest contour coincidence degree of the two dispersion curves set by the first preset curve. As can be seen from FIG. 6, at a wavelength of 4.2 μm of the input pulse signal, the dispersions corresponding to the TE wave and the TM wave are respectively 4.857ps/nm/km and 4.859ps/nm/km, and at this time, the curve coincidence degree is considered to reach the first preset curve coincidence degree.
In some optional embodiments of the present invention, the polarization insensitivity of the algan waveguide may be verified by further combining a first nonlinear coefficient curve and a second nonlinear coefficient curve corresponding to the TE wave and the TM wave output by the algan waveguide structure. As shown in fig. 7, the first nonlinear coefficient curve and the second nonlinear coefficient curve corresponding to the TE wave and the TM wave are almost completely overlapped, where at a pulse signal wavelength of 4.2 μm, the nonlinear coefficients of the first nonlinear coefficient curve corresponding to the TE wave and the second nonlinear coefficient curve corresponding to the TM mode pulse wave are 0.6067/m/W and 0.6057/m/W, respectively, and it can be considered that the curve overlap ratio of the first nonlinear coefficient curve and the second nonlinear coefficient curve reaches a second preset curve overlap ratio, which is the lowest profile overlap ratio of the two nonlinear coefficient curves set for the first nonlinear coefficient curve and the second nonlinear coefficient curve.
In some optional embodiments of the present invention, the polarization insensitivity of the algan waveguide may be verified by further combining the first effective mode area curve and the second effective mode area curve corresponding to the TE wave and the TM wave output by the algan waveguide structure. As shown in fig. 7, the first effective mode area curve and the second effective mode area curve corresponding to the TE wave and the TM wave are almost completely overlapped, that is, the curve overlap ratio of the first effective mode area curve and the second effective mode area curve reaches a third preset curve overlap ratio, which is the lowest contour overlap ratio of the two effective mode area curves set by the user.
In conclusion, curves of chromatic dispersion, nonlinear coefficient and effective mode area corresponding to TE waves and TM waves are highly coincident, and the polarization insensitivity of the AlGaAs waveguide structure designed by the invention is verified.
According to the polarization-insensitive AlGaAs waveguide structure provided by the embodiment of the invention, by reasonably designing the width, the first height and the second height of the light guide layer, the corresponding dispersion curves, nonlinear coefficient curves and effective mode areas of the TE wave and the TM wave can be controlled to be highly superposed, so that the AlGaAs waveguide structure is insensitive to the polarization of an input pulse signal; the polarization mode of the input pulse does not need to be adjusted, the complexity of an experiment system can be reduced, and the experiment efficiency is improved.
For the above-mentioned rationally designed algan waveguide structure, this embodiment further provides a method for generating a supercontinuum by using the algan waveguide structure, where fig. 8 is a flowchart of the method according to the embodiment of the present invention, and as shown in fig. 8, the method includes:
s100, designing the width, the first height, the second height and the length along the light transmission direction of the AlGaAs waveguide structure;
s200, inputting chirp-free hyperbolic secant pulse with a pumping wavelength of 4.2 mu m, a peak power of 4.8kW and a pulse width of 90fs into the AlGaAs waveguide structure, and outputting a first supercontinuum corresponding to the TE wave and a second supercontinuum corresponding to the TM wave, wherein the frequency spectrum coincidence degree of the first supercontinuum and the second supercontinuum reaches a preset frequency spectrum coincidence degree.
In step S100, the width W of the light guiding layer of algan in the algan waveguide structure is 6.95 μm to 7.15 μm, and the first height H 1 In the range of 3.45 μm to 3.6 μm, a second height H 2 The range is 2.95 to 3.4 μm, and the length range is 3.2 to 3.5mm. Optionally, the width of the algan waveguide is 7 μm, the first height is 3.52 μm, the second height is 3.26 μm, and the length L along the light transmission direction is 3.4mm. For other structures, please refer to the description of the algan waveguide structure in the above embodiments, which is not repeated herein.
In step S200, since the input pulse pump wavelength is 4.2 μm, the TE wave and the TM wave are both located in the anomalous dispersion region, so that a high-order soliton can be formed under the action of dispersion and self-phase modulation effect, which is beneficial to the broadening of the spectrum; in addition, the dispersion remains low and flat over a large wavelength range, which causes walk-off of frequency components, further increasing the spectral range; and the spectrum is broadened from the anomalous dispersion region to the normal dispersion region, promoting the formation of dispersion waves.
As shown in fig. 9, after hyperbolic secant pulse signals with wavelength of 4.2 μm, peak power of 4.8kW, pulse width of 90fs and random noise coefficient of 0.001 are incident to the algan waveguide structure designed in step S100, a first supercontinuum corresponding to the TE wave and a second supercontinuum corresponding to the TM wave are obtained by a simulation technique. As can be seen from the figure, at the-40 dB level of the frequency spectrum, the TE wave generates a mid-infrared continuous spectrum with more than 1.95 octaves from 2.17 μm to 8.53 μm, the TM wave generates a mid-infrared supercontinuum with more than 1.95 octaves from 2.23 μm to 8.61 μm, and the supercontinuums corresponding to the two modes are highly overlapped, wherein the preset frequency spectrum overlap ratio is the lowest contour overlap ratio of the two artificially set frequency spectrums.
Fig. 10 shows coherence of supercontinuum of TE wave and TM wave in this example, and it can be seen from the figure that first order coherence of supercontinuum corresponding to both modes of wave is almost kept at 0.9-1 in the considered range, and coherence is good. Therefore, the high-coherence octave broadband supercontinuum can be obtained through the AlGaAs waveguide designed by the invention.
According to the method for generating the supercontinuum by using the AlGaAs waveguide structure, based on the polarization insensitivity characteristic of the AlGaAs waveguide structure, chirp-free hyperbolic secant pulses with the pumping wavelength of 4.2 microns, the peak power of 4.8kW and the pulse width of 90fs are incident to the AlGaAs waveguide, so that the high-coherence octave broadband supercontinuum is generated.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (9)

1. The utility model provides an aluminium gallium arsenic waveguide structure which characterized in that, aluminium gallium arsenic waveguide structure is used for receiving pulse signal and outputs TE ripples and TM ripples, aluminium gallium arsenic waveguide structure includes:
the surface of the AlGaAs substrate is provided with a groove along the light transmission direction;
the AlGaAs light guide layer is arranged in the groove and partially protrudes outwards, the upper surface of the AlGaAs light guide layer is at a first height from the upper surface of the groove, and the lower surface of the AlGaAs light guide layer is at a second height from the upper surface of the groove; wherein the width range of the AlGaAs light guide layer is 6.95-7.15 μm, the first height range is 3.45-3.6 μm, and the second height range is 2.95-3.4 μm;
controlling the curve coincidence degree of a first dispersion curve corresponding to the TE wave and a second dispersion curve corresponding to the TM wave to reach a first preset curve coincidence degree by adjusting the width, the first height and the second height of the AlGaAs light guide layer; the refractive index of the AlGaAs light guide layer is larger than that of the AlGaAs substrate.
2. The AlGaAs waveguide structure of claim 1, wherein the AlGaAs light guiding layer has a rectangular cross section.
3. The AlGaAs waveguide structure of claim 1, wherein the AlGaAs light guiding layer contains 18% by mass of aluminum arsenide and 82% by mass of gallium arsenide.
4. The AlGaAs waveguide structure of claim 1, wherein the AlGaAs light guide layer has a width of 7 μm, a first height of 3.52 μm, and a second height of 3.26 μm.
5. The AlGaAs waveguide structure of claim 1, wherein the AlGaAs substrate comprises 80% by mass of aluminum arsenide and 20% by mass of gallium arsenide.
6. A method of generating a supercontinuum using an algan waveguide structure according to any one of claims 1 to 5, comprising:
designing the width, the first height, the second height and the length along the light transmission direction of the AlGaAs waveguide;
inputting a chirp-free hyperbolic secant pulse with the wavelength of 4.2 mu m, the peak power of 4.8kW and the pulse width of 90fs into the AlGaAs waveguide structure to generate a first supercontinuum corresponding to the TE wave and a second supercontinuum corresponding to the TM wave, wherein the frequency spectrum coincidence ratio of the first supercontinuum and the second supercontinuum reaches a preset frequency spectrum coincidence ratio.
7. The method of claim 6, wherein the AlGaAs waveguide structure has a width in a range of 6.95 μm to 7.15 μm, a first height in a range of 3.45 μm to 3.6 μm, a second height in a range of 2.95 μm to 3.4 μm, and a length in a light transmission direction in a range of 3.2mm to 3.5mm.
8. The method of claim 7, wherein the first supercontinuum and the second supercontinuum each have a broadband wavelength in excess of 1.95 octaves.
9. The method of claim 7, wherein the first order coherence range of the first supercontinuum and the second supercontinuum is between 0.9 and 1 at a frequency spectrum of-40 dB.
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